Android利用LocalSocket实现Java端进程与C端进程之间的IPC

Android是建立在Linux之上的OS，在涉及到安全、网络协议、文件加密等功能时，往往需要通过C语言调用底层API来实现，而如何发出指令让C端执行我们想要的功能，并且在执行之后有返回结果呢，这就需要打通Java端进程和C端进程，使之能高效地通信。这样，C端进程用于实现功能，Java端进程负责UI、功能的触发及结果处理就可以了。

　　对于unix系统来说，“一切皆为文件”，Socket也不例外，Socket按照收发双方的媒介来说有三种类型：1，通过网络端口；2，通过文件系统；3，通过内存映射文件。具体说来，三种类型均可以用来作为IPC的Socket：1，通过本地回环接口(即LoopBack)127.0.0.1来收发数据；2，通过文件作为收发数据的中转站；3，在内存中开辟一块区域作为收发数据的中转站，此区域仍然使用文件读写API进行访问。LocalSocket支持方式2和方式3，从效率的角度来说，显然是方式3效率最高，那么下面我们就使用LocalSocket来演示如何实现Java端进程与C端进程之间的IPC。

　　以下的demo是Java端作为server，C端作为client；实际场景中可能更多的是Java端作为client，而C端作为server。

服务端代码如下：

package main.activity;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import android.app.Activity;
import android.net.LocalServerSocket;
import android.net.LocalSocket;
import android.os.Bundle;
import android.util.Log;

/**
* @author pengyiming
* @note 启动localSocketServer
*
*/

public class LocalSocketServerActivity extends Activity
{
/* 数据段begin */
private final String TAG = "server";

private ServerSocketThread mServerSocketThread;
/* 数据段end */

/* 函数段begin */
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
mServerSocketThread = new ServerSocketThread();
mServerSocketThread.start();
}

@Override
protected void onDestroy()
{
super.onDestroy();
mServerSocketThread.stopRun();
}
/* 函数段end */

/* 内部类begin */
private class ServerSocketThread extends Thread
{
private boolean keepRunning = true;
private LocalServerSocket serverSocket;

private void stopRun()
{
keepRunning = false;
}

@Override
public void run()
{
try
{
serverSocket = new LocalServerSocket("pym_local_socket");
}
catch (IOException e)
{
e.printStackTrace();
keepRunning = false;
}

while(keepRunning)
{
Log.d(TAG, "wait for new client coming !");

try
{
LocalSocket interactClientSocket = serverSocket.accept();

//由于accept()在阻塞时，可能Activity已经finish掉了，所以再次检查keepRunning
if (keepRunning)
{
Log.d(TAG, "new client coming !");
new InteractClientSocketThread(interactClientSocket).start();
}
}
catch (IOException e)
{
e.printStackTrace();
keepRunning = false;
}
}

if (serverSocket != null)
{
try
{
serverSocket.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
}

private class InteractClientSocketThread extends Thread
{
private LocalSocket interactClientSocket;

public InteractClientSocketThread(LocalSocket interactClientSocket)
{
this.interactClientSocket = interactClientSocket;
}

@Override
public void run()
{
StringBuilder recvStrBuilder = new StringBuilder();
InputStream inputStream = null;
try
{
inputStream = interactClientSocket.getInputStream();
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
char[] buf = new char[4096];
int readBytes = -1;
while ((readBytes = inputStreamReader.read(buf)) != -1)
{
String tempStr = new String(buf, 0, readBytes);
recvStrBuilder.append(tempStr);
}
}
catch (IOException e)
{
e.printStackTrace();

Log.d(TAG, "resolve data error !");
}
finally
{
if (inputStream != null)
{
try
{
inputStream.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
}
}
/* 内部类end */
}

客户端代码如下：

package main.activity;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

/**
* @author pengyiming
* @note 用于启动localSocketClient，向server发送心跳报文
*
*/

public class LocalSocketClientActivity extends Activity
{
/* 数据段begin */
private final String TAG = "client";

private HeartBeatThread mHeartBeatThread;

public native int startHeartBeat();
/* 数据段end */

/* 函数段begin */
static
{
System.loadLibrary("pymclient");
}

@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);

mHeartBeatThread = new HeartBeatThread();
mHeartBeatThread.start();
}

@Override
protected void onDestroy()
{
super.onDestroy();

mHeartBeatThread.stopRun();
}
/* 函数段end */

/* 内部类begin */
private class HeartBeatThread extends Thread
{
int ret;
boolean keepRunning = true;

public void stopRun()
{
keepRunning = false;
}

@Override
public void run()
{
Log.d(TAG, "start heart beat!");

while (keepRunning)
{
ret = startHeartBeat();

Log.d(TAG, "ret = " + ret);

if (ret != 0)
{
break;
}

try
{
sleep(1000);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}

Log.d(TAG, "stop heart beat!");
}
}
/* 内部类end */
}

上述客户端代码启动了一个线程用于发送“心跳”报文，每隔1s构建一个新的LocalSocket，连接服务端并发送流数据，其核心就在于native方法的实现。值得一提的是，我最初使用原生socket函数，没想connect总是返回错误；后来在同事的提醒下，我参考了Android源码rild.c中socket_local_client的使用，并从socket_local_client.c中抽取出相应代码改写而成。

客户端native方法头文件：

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class main_activity_LocalSocketClientActivity */

#ifndef _Included_main_activity_LocalSocketClientActivity
#define _Included_main_activity_LocalSocketClientActivity
#ifdef __cplusplus
extern "C" {
#endif

/* socket命名空间(见cutils/sockets.h) */
#define ANDROID_SOCKET_NAMESPACE_ABSTRACT 0
#define ANDROID_SOCKET_NAMESPACE_RESERVED 1
#define ANDROID_SOCKET_NAMESPACE_FILESYSTEM 2

/* socket类型 */
#define SOCK_STREAM      1
#define SOCK_DGRAM       2
#define SOCK_RAW         3
#define SOCK_RDM         4
#define SOCK_SEQPACKET   5
#define SOCK_PACKET      10

/* 清0宏 */
#define MEM_ZERO(pDest, destSize) memset(pDest, 0, destSize)

/* 错误码定义 */
#define NO_ERR 0
#define CREATE_ERR -1
#define CONNECT_ERR -2
#define LINUX_MAKE_ADDRUN_ERROR -3
#define NO_LINUX_MAKE_ADDRUN_ERROR -4
#define CLOSE_ERR -5

/* 是否使用linux的本地socket命令空间 */
#define HAVE_LINUX_LOCAL_SOCKET_NAMESPACE "linux_local_socket_namespace"

#undef main_activity_LocalSocketClientActivity_MODE_PRIVATE
#define main_activity_LocalSocketClientActivity_MODE_PRIVATE 0L
#undef main_activity_LocalSocketClientActivity_MODE_WORLD_READABLE
#define main_activity_LocalSocketClientActivity_MODE_WORLD_READABLE 1L
#undef main_activity_LocalSocketClientActivity_MODE_WORLD_WRITEABLE
#define main_activity_LocalSocketClientActivity_MODE_WORLD_WRITEABLE 2L
#undef main_activity_LocalSocketClientActivity_MODE_APPEND
#define main_activity_LocalSocketClientActivity_MODE_APPEND 32768L
#undef main_activity_LocalSocketClientActivity_MODE_MULTI_PROCESS
#define main_activity_LocalSocketClientActivity_MODE_MULTI_PROCESS 4L
#undef main_activity_LocalSocketClientActivity_BIND_AUTO_CREATE
#define main_activity_LocalSocketClientActivity_BIND_AUTO_CREATE 1L
#undef main_activity_LocalSocketClientActivity_BIND_DEBUG_UNBIND
#define main_activity_LocalSocketClientActivity_BIND_DEBUG_UNBIND 2L
#undef main_activity_LocalSocketClientActivity_BIND_NOT_FOREGROUND
#define main_activity_LocalSocketClientActivity_BIND_NOT_FOREGROUND 4L
#undef main_activity_LocalSocketClientActivity_BIND_ABOVE_CLIENT
#define main_activity_LocalSocketClientActivity_BIND_ABOVE_CLIENT 8L
#undef main_activity_LocalSocketClientActivity_BIND_ALLOW_OOM_MANAGEMENT
#define main_activity_LocalSocketClientActivity_BIND_ALLOW_OOM_MANAGEMENT 16L
#undef main_activity_LocalSocketClientActivity_BIND_WAIVE_PRIORITY
#define main_activity_LocalSocketClientActivity_BIND_WAIVE_PRIORITY 32L
#undef main_activity_LocalSocketClientActivity_BIND_IMPORTANT
#define main_activity_LocalSocketClientActivity_BIND_IMPORTANT 64L
#undef main_activity_LocalSocketClientActivity_BIND_ADJUST_WITH_ACTIVITY
#define main_activity_LocalSocketClientActivity_BIND_ADJUST_WITH_ACTIVITY 128L
#undef main_activity_LocalSocketClientActivity_CONTEXT_INCLUDE_CODE
#define main_activity_LocalSocketClientActivity_CONTEXT_INCLUDE_CODE 1L
#undef main_activity_LocalSocketClientActivity_CONTEXT_IGNORE_SECURITY
#define main_activity_LocalSocketClientActivity_CONTEXT_IGNORE_SECURITY 2L
#undef main_activity_LocalSocketClientActivity_CONTEXT_RESTRICTED
#define main_activity_LocalSocketClientActivity_CONTEXT_RESTRICTED 4L
#undef main_activity_LocalSocketClientActivity_RESULT_CANCELED
#define main_activity_LocalSocketClientActivity_RESULT_CANCELED 0L
#undef main_activity_LocalSocketClientActivity_RESULT_OK
#define main_activity_LocalSocketClientActivity_RESULT_OK -1L
#undef main_activity_LocalSocketClientActivity_RESULT_FIRST_USER
#define main_activity_LocalSocketClientActivity_RESULT_FIRST_USER 1L
#undef main_activity_LocalSocketClientActivity_DEFAULT_KEYS_DISABLE
#define main_activity_LocalSocketClientActivity_DEFAULT_KEYS_DISABLE 0L
#undef main_activity_LocalSocketClientActivity_DEFAULT_KEYS_DIALER
#define main_activity_LocalSocketClientActivity_DEFAULT_KEYS_DIALER 1L
#undef main_activity_LocalSocketClientActivity_DEFAULT_KEYS_SHORTCUT
#define main_activity_LocalSocketClientActivity_DEFAULT_KEYS_SHORTCUT 2L
#undef main_activity_LocalSocketClientActivity_DEFAULT_KEYS_SEARCH_LOCAL
#define main_activity_LocalSocketClientActivity_DEFAULT_KEYS_SEARCH_LOCAL 3L
#undef main_activity_LocalSocketClientActivity_DEFAULT_KEYS_SEARCH_GLOBAL
#define main_activity_LocalSocketClientActivity_DEFAULT_KEYS_SEARCH_GLOBAL 4L
/*
* Class:     main_activity_LocalSocketClientActivity
* Method:    startHeartBeat
* Signature: ()I
*/
JNIEXPORT jint JNICALL Java_main_activity_LocalSocketClientActivity_startHeartBeat
(JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

客户端native方法实现：

/* 头文件begin */
#include "main_activity_LocalSocketClientActivity.h"

#include <sys/socket.h>
#include <sys/un.h>
#include <stddef.h>
#include <string.h>
/* 头文件end */

#ifdef __cplusplus
extern "C" {
#endif

/*
* Class:     main_activity_LocalSocketClientActivity
* Method:    startHeartBeat
*/
JNIEXPORT jint JNICALL Java_main_activity_LocalSocketClientActivity_startHeartBeat(JNIEnv * env, jobject object)
{
int socketID;
struct sockaddr_un serverAddr;
char path[] = "pym_local_socket\0";
int ret;

socketID = socket_local_client(path, ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_STREAM);
if (socketID < 0)
{
return socketID;
}

ret = close(socketID);
if (ret < 0)
{
return CLOSE_ERR;
}

return NO_ERR;
}

/* 创建本地socket客户端 */
int socket_local_client(const char *name, int namespaceId, int type)
{
int socketID;
int ret;

socketID = socket(AF_LOCAL, type, 0);
if(socketID < 0)
{
return CREATE_ERR;
}

ret = socket_local_client_connect(socketID, name, namespaceId, type);
if (ret < 0)
{
close(socketID);

return ret;
}

return socketID;
}

/* 连接到相应的fileDescriptor上 */
int socket_local_client_connect(int fd, const char *name, int namespaceId, int type)
{
struct sockaddr_un addr;
socklen_t socklen;
size_t namelen;
int ret;

ret = socket_make_sockaddr_un(name, namespaceId, &addr, &socklen);
if (ret < 0)
{
return ret;
}

if(connect(fd, (struct sockaddr *) &addr, socklen) < 0)
{
return CONNECT_ERR;
}

return fd;
}

/* 构造sockaddr_un */
int socket_make_sockaddr_un(const char *name, int namespaceId, struct sockaddr_un *p_addr, socklen_t *socklen)
{
size_t namelen;

MEM_ZERO(p_addr, sizeof(*p_addr));
#ifdef HAVE_LINUX_LOCAL_SOCKET_NAMESPACE

namelen  = strlen(name);

// Test with length +1 for the *initial* '\0'.
if ((namelen + 1) > sizeof(p_addr->sun_path))
{
return LINUX_MAKE_ADDRUN_ERROR;
}
p_addr->sun_path[0] = 0;
memcpy(p_addr->sun_path + 1, name, namelen);

#else

namelen = strlen(name) + strlen(FILESYSTEM_SOCKET_PREFIX);

/* unix_path_max appears to be missing on linux */
if (namelen > (sizeof(*p_addr) - offsetof(struct sockaddr_un, sun_path) - 1))
{
return NO_LINUX_MAKE_ADDRUN_ERROR;
}

strcpy(p_addr->sun_path, FILESYSTEM_SOCKET_PREFIX);
strcat(p_addr->sun_path, name);

#endif

p_addr->sun_family = AF_LOCAL;
*socklen = namelen + offsetof(struct sockaddr_un, sun_path) + 1;

return NO_ERR;
}

#ifdef __cplusplus
}
#endif

注意到100~101行比较特殊，是从p_addr->sun_path[1]开始拷贝本地域名，这就是之前为什么一直connect不上的原因，至于为什么偏移1个字节来拷贝本地域名，你可以在unix系统下输入"man 7 unix"来找到原因。

　　先启动server，再启动client就可以看到结果了。对了，在成功创建并已自动连接后，我并未发送任何数据，其实发送数据就是写入文件，It's your trun now! 在close之前加入这段代码吧~

int ret;
char buf[] = "hello";

ret = write(socketID, buf, strlen(buf));